Vacuum relief valve for sewage holding tank

Abstract

A plastic sewage holding tank in a boat, associated with a toilet, includes a vent check valve assembly for providing vacuum relief. By mounting the vent check valve in the top of the tank, when the tank is being emptied by rapid pumpout implosion or other damage to the tank is prevented. The vent check valve assembly may include a valve body surface operatively connected to the tank and having a plurality of openings formed in it, and a flexible material diaphragm covering the openings adjacent the inside of the tank, and uncovering openings to allow air flow through the openings substantially only when a vacuum condition exists inside the tank. A plastic disk biases the diaphragm into its opening-covering position, but a partial vacuum of at least about 2-5 inches of water allows air to flow through the openings past the diaphragm.

What is claimed is: 
     
       1. A boat assembly, comprising: a boat hull defining an interior boat volume;   a toilet within the interior boat volume;   a sewage holding tank operatively connected to said toilet, and also within said interior boat volume, said tank having an inside;   an outlet conduit from said holding tank, and including a dockside pumpout fitting;   an indicator of the fullness of said holding tank at at least one level of fullness thereof;   a gas vent from said holding tank; and   a vacuum relief valve assembly for said holding tank to prevent adverse consequences associated with a vacuum condition in said tank said valve assembly comprising a valve body surface operatively connected to said tank and having a plurality of openings formed therein, a flexible material diaphragm covering said openings adjacent said inside of said tank, and uncovering openings to allow air flow therethrough substantially only when a vacuum condition exists inside said tank; and   a support element mounted in contact with said flexible material diaphragm and providing a force on said diaphragm to releasably maintain said diaphragm in a position covering said openings.   
     
     
       2. A boat assembly as recited in claim 1 wherein said vacuum relief valve is constructed and configured so that said flexible material diaphragm uncovers openings to allow air flow therethrough when the vacuum within said holding tank is as low as about 2-5 inches of water, and substantially prevents spitting. 
     
     
       3. A boat assembly as recited in claim 1 wherein said flexible material diaphragm is a substantially circular disk, and wherein said support element is also a substantially circular disk having a diameter less than the diameter of said flexible material diaphragm. 
     
     
       4. A boat assembly as recited in claim 1 wherein said disks are releasably held to said valve body with a fastener assembly. 
     
     
       5. A boat assembly as recited in claim 1 further comprising a splash protector disk mounted to said valve body on the opposite side of said diaphragm and support element from said openings. 
     
     
       6. An assembly as recited in claim 1 wherein said plurality of openings comprise a plurality of openings of at least two different cross sectional areas including smaller cross sectional area openings around the periphery of said valve body. 
     
     
       7. An assembly as recited in claim 1 wherein said plurality of openings comprise a plurality of openings of at least two different cross sectional areas including smaller cross sectional area openings around the periphery of said valve body, said smaller cross sectional area openings being circular; and wherein the difference in diameter between said diaphragm and said support disk is approximately equal to the radius of said small openings. 
     
     
       8. A boat assembly as recited in claim 1 wherein said diaphragm is of an elastomeric material having a shore A durometer of about 50-70 and a thickness of about 0.055-0.075 inches and wherein said support disk comprises, or is equivalent to, a polypropylene disk having a thickness of between about 0.010-0.020 inches; and wherein said diaphragm has a diameter of between about 1.85-2.05 inches, and said polypropylene disk has a diameter of between about 1.65-1.95 inches. 
     
     
       9. A sewage holding tank assembly comprising: a plastic sewage holding tank having a top and a bottom, a hollow interior, and an exterior;   an outlet conduit from said holding tank and including a dockside pumpout fitting;   a vent for said holding tank, adjacent said top thereof for allowing passage of gas under pressure from said tank to the exterior thereof;   an inlet conduit for feeding sewage into said holding tank; and   a vent check valve assembly mounted to said holding tank top for allowing passage of air from exterior of said tank to the interior of said tank when a significant vacuum condition exists within said tank, said valve assembly comprising a valve body surface operatively connected to said tank and having a plurality of openings formed therein, a flexible material diaphragm covering said openings adjacent said inside of said tank, and uncovering openings to allow air flow therethrough substantially only when a vacuum condition exists inside said tank; and   wherein said valve assembly is mounted to said holding tank by a peripheral upper lip on said valve body, substantially all of said valve body disposed within said tank hollow interior.   
     
     
       10. A holding tank assembly as recited in claim 9 wherein said valve assembly is constructed and configured so that said flexible material diaphragm uncovers openings to allow air flow therethrough when the vacuum within said holding tank is as low as about 2-5 inches of water, and substantially prevents spitting. 
     
     
       11. A holding tank assembly as recited in claim 9 wherein said valve assembly is constructed and configured so that said flexible material diaphragm uncovers openings to allow air flow therethrough when the vacuum within said holding tank is as low as about 2-5 inches of water, and substantially prevents spitting. 
     
     
       12. A holding tank assembly as recited in claim 9 wherein said valve assembly further comprises a support element mounted in contact with said flexible material diaphragm and providing a force on said diaphragm to releasably maintain said diaphragm in a position covering said openings. 
     
     
       13. A vent check valve assembly comprising: a valve body comprising a tubular plastic element having an open top first end and an open bottom second end, a valve body surface disposed between said top and bottom and having a plurality of openings formed therein;   an elastomeric material valve disk having a substantially circular configuration covering said openings adjacent said second end of said valve body;   a flexible support disk of relatively stiff material engaging said valve disk and releasably holding said valve disk in a position covering said openings; and   a fastener assembly for releasably holding said valve disk and said support disk entrapped within said valve body surface;   said support disk having a diameter about 85-96% that of said valve disk element.   
     
     
       14. A valve assembly as recited in claim 13 wherein said diaphragm is of an elastomeric material having a shore A durometer of about 50-70 and a thickness of about 0.055-0.075 inches and wherein said support disk comprises, or is equivalent to, a polypropylene disk having a thickness of between about 0.010-0.020 inches; and wherein said diaphragm has a diameter of between about 1.85-2.05 inches, and said polypropylene disk has a diameter of between about 1.65-1.95 inches and wherein said plurality of openings comprise a plurality of openings of at least two different cross sectional areas including smaller cross sectional area openings around the periphery of said valve body, said smaller cross sectional area openings being circular; and wherein the difference in diameter between said diaphragm and said support disk is approximately equal to the radius of said smaller openings. 
     
     
       15. A sewage holding tank assembly comprising: a plastic sewage holding tank having a top and a bottom, a hollow interior, and an exterior;   an outlet conduit from said holding tank and including a dockside pumpout fitting;   a vent for said holding tank, adjacent said top thereof for allowing passage of gas under pressure from said tank to the exterior thereof;   an inlet conduit for feeding sewage into said holding tank; and   a vent check valve assembly mounted to said holding tank top for allowing passage of air from exterior of said tank to the interior of said tank when a significant vacuum condition exists within said tank, said valve assembly comprising a valve body surface operatively connected to said tank and having a plurality of openings formed therein, and a flexible material diaphragm covering said openings adjacent said inside of said tank, and uncovering openings to allow air flow therethrough substantially only when a vacuum condition exists inside said tank, and a support element mounted in contact with said flexible material diaphragm and providing a force on said diaphragm to releasably maintain said diaphragm in a position covering said openings.   
     
     
       16. A holding tank assembly as recited in claim 12 wherein said flexible material diaphragm is a substantially circular disk, and wherein said support element is also a substantially circular disk having a diameter less than the diameter of said flexible material diaphragm. 
     
     
       17. A holding tank assembly as recited in claim 13 wherein said disks are releasably held to said valve body with a fastener assembly. 
     
     
       18. A holding tank assembly as recited in claim 17 wherein said plurality of openings comprise a plurality of openings of at least two different cross sectional areas including smaller cross sectional area openings around the periphery of said valve body, said smaller cross sectional area openings being circular; and wherein the difference in diameter between said diaphragm and said support disk is approximately equal to the radius of said smaller openings. 
     
     
       19. A holding tank assembly as recited in claim 17 further comprising a splash protector disk mounted to said valve body on the opposite side of said diaphragm and support element from said openings. 
     
     
       20. A holding tank assembly as recited in claim 17 wherein said diaphragm is of an elastomeric material having a shore A durometer of about 50-70 and a thickness of about 0.055-0.075 inches and wherein said support disk comprises, or is equivalent to, a polypropylene disk having a thickness of between about 0.010-0.020 inches; and wherein said diaphragm has a diameter of between about 1.85-2.05 inches, and said polypropylene disk has a diameter of between about 1.65-1.95 inches.